The identification of disease genes and their protein products has led to research on gene therapy techniques. In gene therapy, normal genes are inserted into cells to replace defective genes that cause disease (perhaps because they produce an abnormal type of a crucial protein). Although many different researchers around the world are investigating gene therapy techniques to treat a wide variety of diseases (see box) gene therapy is still experimental. Concerns have been raised about the generally short-term nature of the treatment (the cells in the body that receive the altered genes will eventually die, so the therapy has to be repeated); potential immune responses, which might recognize the genetically altered cells as foreign; and concerns about the safety of the viruses usually used to transfer the modified genes.

The Food and Drug Administration has not approved any gene therapy product for sale.